There’s plenty of disagreement and controversy at the moment, so let me stoke things a bit more:

Light Mode is better than Dark Mode (for me)

Here’s why, with some science behind it, too. Yes, I have a justification as well just a preference…

Let’s start with what we know:
The pupil of the eye shrinks when there’s a lot of light and dilates when it’s darker

The question is: how much difference will it make between viewing a screen in dark mode and light mode?

Here’s a very rough, crude experiment (emphasis on “rough” and “crude”, and use of “experiment” is very loose here!)

Details in next toot


I used PyCharm’s Darcula and IntelliJ Light themes on a 27” screen — PyCharm was in full screen mode. iMac was on 75% brightness (usual setting)

I stood in my normal position—arm’s length from screen—and looked at the middle of the screen…

Here’s my eye pupil as I switch from dark mode to light mode

Video quality not great (don’t view in full screen!!)—but this is just a rough experiment, so it will do nicely

And you can see stills, with a very rough estimate of the relative pupil sizes, in the first toot…

On the right you’ll see the small pupil from the light mode scenario shown in red and superimposed on the black “dark mode” pupil


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Every eye has aberrations, or imperfections…

…and these are not just the ones we correct using glasses or contact lenses.

Those are just the main ones.

The others are called higher-order aberrations.

The larger the pupil of the eye, the more higher-order aberrations there are.

Therefore, in bright lights, when the pupils are small, there aren’t many higher order aberrations…

But when the light levels are low and the pupils large, there are significantly more.

Everyone has higher-order aberrations, but not everyone has the same amount.

So this is worse for some people.

I happen to know that I have reasonably high higher-order aberrations (How do I know this: from my previous work as a scientist when I often measured these)

More aberrations = lower resolution and lower contrast = poorer vision.


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How about diffraction?

Diffraction is something completely different… It’s a fundamental optical phenomenon

All optical systems suffer from this, even ones that have no aberrations (imperfections)

Small pupils lead to more diffraction which reduces resolution.

Large pupils have less diffraction and therefore have less of an effect on resolution.

This is why telescopes have large diameters and professional photographers have lenses with larger diameters.


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So, in the human eye, there is an optimum pupil size. If the pupil is very small, diffraction leads to lower resolution…

If the pupil is too large, higher-order aberrations lead to lower resolution.

The sweet spot varies from person to person (it’s roughly around 3-5mm — the pupil typically can vary between 2-8mm in an average eye)


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Back to dark and light modes.

For someone with high higher-order aberrations (like me), dark mode pushes the pupil size well above the ideal pupil size, therefore vision is worse.

This will not be the case for everyone, of course.

But, dark mode is not for everyone…

If, like me, you prefer light mode, ignore all those who snigger because “pros use dark mode”


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interesting reasoning, maybe I'll change to light some day :thaenkin: thanks

@Santiag0 it doesn’t mean it applies to all, though. We all have different levels of higher-order aberrations, and our pupil sizes change by different amounts

@s_gruppetta I'm using dark mode everywhere, but honestly, "pros use dark mode" is such a BS... Thanks for a very informative thread.


It was a well reasoned and interesting breakdown of the human eye, so I think you'll be fine without protection. ;p

@s_gruppetta dude I love your study of this, have you compared the differences by environmental brightness and display type as well. For instance, 3200 lumen window brightness and 500 nit LCD, and 100 lumen environmental brightness and 600 nit AMOLED would be almost intolerable. But under the right environmental conditions would be pretty much required. I’ve always thought the best scenario for a programmer would be a monochromatic paper LCD like on e-readers if they could get the response time higher. On those displays, light mode or dark mode doesn’t seem to affect eye strain at all. Thanks for the thought provocations 🤔

@s_gruppetta lol but you could say the same about being a py programmer in general:-)

@s_gruppetta I’d like to use light mode, but I have eye floaters and it’s really annoying and distracting.

@anmomu92 that’s in part the point of my thread. Different people need different modes, there’s no one size fits all

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